Manufacture of reinforced asbestos-cement pipes



0m. 4, 1955 P. DESNOS ,7 ,34

MANUFACTURE OF REINFORCED ASBESTOS-CEMENT PIPES Filed March 28, 1952 INVENTO/Q PIERRE DES/W29 Aa-y.

United States Patent MANUFACTURE OF REINFORCED ASBESTOS-CEMENT PIPES Pierre Desnos, Paris, France, assignor to Societe Anonyme Francaise Eternit, Paris, France, a French company Application March 28, 1952, Serial No. 279,179

Claims priority, application France March 30, 1951 2 Claims. (Cl. 25-154) Asbestos-cement pipes intended for uses in which there is no pressure involved are normally made rela tively thin in order to economise in material, such pipes nevertheless being capable of ensuring complete fluidtightness even though of small thickness. There are however many uses in which the requirement for resistance to external forces (such as crushing) renders necessary the manufacture of thicker pipes, the cost of the materials involved considerably increasing the expense of such manufacture.

The present invention obviates this disadvantage by the provision of a composite pipe comprising only a small thickness of asbestos-cement, thus permitting economy in the relatively expensive materials, but which includes an internal or external covering of a considerably cheaper material so chosen as to increase the resistance of the pipe to crushing up to any desired degree.

According to one form of the invention an asbestoscement pipe is provided either internally or externally with a concrete lining which constitutes a refinforcing layer, in such a manner that the composite pipe preserves all the qualities of an asbestos-cement pipe but can be strengthened to any desired degree by this relatively cheap covering of concrete.

The invention includes numerous modes of application of this process of manufacture and provides a number of different constructional forms of composite pipes.

Figures 1 to of the accompanying drawing show by way of non-limiting example, in elevation or in half section, several constructions of pipe in accordance with the invention.

As shown in Figure 1 an asbestos-cement pipe 1 is manufactured by any of the conventional methods and is utilised in the dry state. This pipe is placed in a machine whereby it may be placed in rapid rotary movement, either vertical or horizontal. Liquid concrete is introduced at one end of the asbestos-cement pipe, which is set in rotation. The resulting centrifugal force applies the concrete to the inner surface of the asbestoscement pipe, which serves as a mould, so as to constitute a lining of concrete 2. The introduction of the concrete and the rotation of the pipe are continued until the desired thickness of lining 2 has been obtained.

Since the asbestos-cement pipe has a relatively thin wall, the centrifuging of the concrete exerts a force upon the slightly elastic asbestos-cement envelope and slightly extends the latter during the formation of the concrete lining. When the centrifuging is complete, this envelope returns to its initial shape and exerts a pressure on the interior concrete lining which compensates for the normal shrinkage of the latter on drying, and exerts upon it a certain compression, thus ensuring a strong cohesion of the concrete lining to the asbestos-cement pipe.

The sections 1, 1a of the pipe can be assembled by means of a joint 3 made, for example, of asphalt-impregnated felt or the like.

Referring to Figure 2, there is first of all formed a centrifuged concrete pipe 4, which may be reinforced, if

2,719,348 Patented Oct. 4, 1955 21 desired, in accordance with the usual method of manufacture by centrifuging in a steel mould; this pipe may be made of concrete only or may include dry asbestoscement Waste.

There is then introduced into this tube of green con crete an asbestos-cement pipe 5, freshly manufactured, and having an external diameter very close to the internal diameter of the cencrete tube. The centrifuging machine is then again set in motion, so that the asbestoscement pipe, which is still plastic, is deformed under the action of centrifugal force and is applied closely against the concrete tube.

After this step, the composite member is taken out of the machine and dried. The sections 4, 4a of such a tube can be assembled together by means of joints 6 of asphalt-impregnated felt, for example.

Referring to Figure 3, a freshly-made and still plastic asbestos-cement pipe 7 is centrifuged in a metal mould, and while it is still in its freshly-made state, a concrete lining 8 is moulded against its inner surface by centrifuging. The sections 7, 7a of pipe are assembled to gether by a joint 9 which covers the inner surfaces of the ends of the two sections and then a ring 10 of asbestos-cement is formed on the interior of the joint 9, which may be of asphalt-impregnated felt, in order to preserve the same.

Referring to Figure 4, there is first of all employed an asbestos-cement pipe 11 in the dry state made in accordance with any normal manufacturing process. This pipe serves as a housing within which a concrete lining 12 may be applied by centrifuging to the inner surface of the pipe. Thereafter, a lining 13 of freshly-manufactured asbestos-cement is introduced into the pipe 11 and deformed by centrifuging against the inner surface of the concrete layer. There is thus obtained a pipe having both internal and external surfaces of asbestos-cement but which includes an intermediate reinforcing layer of concrete.

Referring to Figure 5, there is employed a mould comprised by a steel tube 14, in which there is formed by centrifuging an asbestos-cement pipe 15, then an inner concrete lining 16 is similarly formed by centrifuging against the inner surface of the asbestos-cement pipe.

It is to be understood that in the preceding description it is intended to include in the term concrete all suitable fluid materials capable of being moulded by centrifuging.

Reinforcing wires can be disposed within the mould or within the asbestos-cement pipe, so as to be embedded in the centrifuged concrete. These reinforcements may be provided with an initial tension so as to apply a precompression to the concrete layer.

The invention is not limited to the examples of its embodiments hereinabove described, numerous modifications thereof being possible without departing from the spirit thereof.

I claim:

1. A process for manufacturing of composite pipes, comprising making a pipe of asbestos cement, drying said pipe, introducing fluid concrete into said pipe, centrifuging said pipe with said fluid concrete therein to expand the asbestos cement of said pipe and force the fluid concrete into intimate contact therewith, continuing said centrifuging until the cement has set, and removing said pipe from centrifugal action to contract the asbestos cement of said pipe and compress the inner concrete coating.

2. A process for manufacturing of composite pipes, comprising introducing fresh concrete into a dry pipe formed of asbestos cement, centrifuging said pipe to expand the asbestos cement thereof and to spread the fresh concrete over the inner surface of said pipe and 3 into intimate contact therewith, continuing said centrifuging until the cement has set, inserting a tube of fresh asbestos cement into said pipe, and centrifuging said pipe to deform said tube into intimate contact with the concrete layer.

References Cited in the file of this patent UNITED STATES PATENTS Siegwart May 28, 1912 4 Overvad Dec. 21, 1937 Whitacre July 30, 1940 Lewis Dec. 15, 1942 Hume Feb. 2, 1943 Fitzpatrick June 28, 1949 Munger July 25, 1950 FOREIGN PATENTS Italy July 25, 1933 

1. A PROCESS FOR MANUFACTURING OF COMPOSITE PIPES, COMPRISING MAKING A PIPE OF ASBESTOS CEMENT, DRYING SAID PIPE, INTRODUCING FLUID CONCRETE INTO SAID PIPE, CENTRIFUGING SAID PIPE WITH SAID FLUID CONCRETE THEREIN TO EXPAND THE ASBESTOS CEMENT OF SAID PIPE AND FORCE THE FLUID CONCRETE INTO INTIMATE CONTACT THEREWITH, CONTINUING SAID CENTRIFUGING UNTIL THE CEMENT HAS SET, AND REMOVING SAID PIPE FROM CENTRIFUGAL ACTION TO CONTRACT THE ASBESTO CEMENT OF SAID PIPE AND COMPRESS THE INNER CONCRETE COATING. 